Network And Internet Application

Network And Internet Application

Lecture-05  Contents – – – –

Token Ring FDDI Bridge Switch

Token Ring    

IBM developed the first Token Ring network in the 1970s. The term Token Ring refers both, to IBM's Token Ring and to IEEE's 802.5 specification. Token-passing access method. Token-passing networks move a small frame, called a token, around the network.

Tokens  

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Tokens are 3 bytes in length. It consist of a start delimiter, an access control byte, and an end delimiter The start delimiter alerts each station to the arrival of a token, or data/command frame. The access control byte contains the priority and reservation field, and a token and monitor bit. The end delimiter signals the end of the token or data/command frame.

Token Passing    

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Possession of the token grants the right to transmit data. If a node that receives a token has no information to send, it passes the token to the next end station. Each station can hold the token for a maximum period of time. When a station passes a token that has information to transmit, it seizes the token and alters 1 bit of it. The token becomes a start-of-frame sequence. There is no token on the network while the information frame is circling the ring. Other stations on the ring cannot transmit at this time. They must wait for the token to become available.

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The information frame circulates the ring until it reaches the intended destination station. The information frame circles the ring until it reaches the sending station and is then removed. The sending station can verify whether the frame was received and copied by the destination.

Priority System    

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Token Ring networks use a sophisticated priority system that permits certain user-designated. Token Ring frames have two fields that control priority - the priority field and the reservation field. Only stations with a priority equal to, or higher than, the priority value contained in a token can seize that token. Once the token has been seized and changed to an information frame, only stations with a priority value higher than that station can reserve the token for the next network pass. Stations that raise a token's priority level must reinstate the previous priority when their transmission has been completed.

Management Mechanisms 

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Token Ring networks use several mechanisms for maintenance one of the mechanism is the active monitor. The active monitor station can potentially be any station on the network. One of this station’s functions is to remove continuously circulating frames from the ring. The active monitor can detect these frames, remove them from the ring, and generate a new token.

FDDI     

Fiber Distributed Data Interface FDDI specifies a 100 Mbps, token-passing, dual-ring LAN that uses a fiber-optic transmission medium. FDDI uses a token passing strategy similar to Token Ring. FDDI use optical fiber as a transmission medium. Optical fiber offers several advantages such as: security - Fiber does not emit electrical signals that can be tapped. reliability - Fiber is immune to electrical interference. speed - Optical fiber has much higher throughput potential than copper cable.

… FDDI   

FDDI specifies the use of dual rings for physical connections. Traffic on each ring travels in opposite directions. FDDI defines the two specified types of fiber: – –

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single-mode multi-mode.

Single-mode fiber allows only one mode of light to propagate through the fiber Multi-mode fiber allows multiple modes of light to propagate through the fiber. Multiple modes of light has different entry angles this causes them to arrive at the destination at different times.

… FDDI 

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Single-mode fiber is capable of higher bandwidth, and greater cable run distances. Single-mode fiber is often used for interbuilding connectivity Multi-mode fiber is often used for intrabuilding connectivity.

FDDI Standards  FDDI

has four specifications:

Media Access Control (MAC) - defines how the medium is accessed. Physical Layer Protocol (PHY) - defines data encoding/decoding procedures. Physical Layer Medium (PMD) - defines the characteristics of the transmission medium. Station Management (SMT) - defines the FDDI station configuration.

… FDDI

FDDI Format  

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preamble - prepares each station for the upcoming frame start delimiter - indicates the beginning of the frame, and consists of signaling patterns that differentiate it from the rest of the frame frame control - indicates the size of the address fields, whether the frame contains asynchronous or synchronous data, and other control information destination address - contains a unicast (singular), multicast (group), or broadcast (every station) address; destination addresses are 6 bytes. source address - identifies the single station that sent the frame; source addresses are 6 bytes.

FDDI Format  

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data - control information, or information destined for an upperlayer protocol frame check sequence (FCS) - filled by the source station with a calculated cyclic redundancy check (CRC), value dependent on the frame contents (as with Token Ring and Ethernet). The destination station recalculates the value to determine whether the frame may have been damaged in transit. If it has been, the frame is discarded. end delimiter - contains non-data symbols that indicate the end of the frame frame status - allows the source station to determine if an error occurred and if the frame was recognized and copied by a receiving station.

BRIDGE  Bridge

connects and passes packets between two network segments that use the same communications protocol.  Bridges operate at the data link layer.  A bridge will filter, forward, or flood an incoming frame based on the MAC address of that frame.

… BRIDGE

SWITCH  A switch

is a layer 2 device.  Switch can be called as a multi-port bridge.  Switches make a LAN much more efficient. They do this by "switching" data only out the port to which the proper host is connected.  By using switches a network behaves like it only has two nodes.  It provides each ports full bandwidth.

… SWITCH

… SWITCH